A common crippling ailment of children is an unstable hip joint, i.e. the femoral head or ball of the hip joint does not maintain a normal congruent relationship with the acetabulum or socket defined in the ilium receiving the femoral head. Such instability may occur due to a shallowness of the socket, an abnormal shape of the femoral head; an abnormal geometrical relationship between the femoral head and neck shaft of the femur; a loosening of the retaining joint capsule and ligaments of the joint; an imbalance in the normal muscle or joint forces, or a combination of these factors.
In the past, a number of medical procedures have been developed to overcome an unstable hip joint condition. For instance, the muscle forces may be redirected, the geometry of the femur may be altered to change the direction of force application through the femoral head or the socket may be deepened by extending the rim by the use of bone as commonly referred to as a shelf procedure. Each of these procedures has limitations which are overcome by the practice of the invention.
The desired prosthesis is designed as an augmentative device to be primarily used in children, and is distinct from replacement devices such as those used for acetabular, femoral head or total hip joint replacement.
The object of the invention is to provide an extracapsular curvalinear prosthesis constructed of a high density synthetic material which artificially enhances the depth of the acetabulum and thereby the ability to retain the femoral head, rendering an unstable hip joint stable. The prosthesis is particularly suitable for use with children minimizing the extend of surgery required.
In the practice of the invention a prosthesis formed of a high density polyethylene is attached by staples, screws or other conventional fasteners to the ilium adjacent to the acetabulum. The prosthesis includes an inner concave socket surface corresponding to the femoral head receiving surface of the acetabulum wherein the attachment of the prosthesis to the ilium enhances the depth of the acetabulum as the prosthesis extends beyond the acetabular rim.
The prosthesis is of sufficient configuration as to extend beyond the acetabular rim laterally, posteriorly and superiorly, and adds a sufficient additional shelf for engagement with the femoral head to render a previously unstable hip joint stable.
The prosthesis is of a configuration to be extracapsular and serves as an adjunct to the existing acetabular socket, but does not replace the socket as with a conventional total hip prosthesis. The configuration of the prosthesis obviates the necessity for accurate geometrical fit as is required with a total joint prosthesis in that the natural acetabulum will continue to define the geometry with respect to the femoral head. The prosthesis can be applied to young children wherein the acetabulum is still growing without adversely affecting the growth process.